The Megalithic Monuments of Arles-Fontvieille and Astronomy in the Neolithic: the winter solstice, equinoxes, and evidence of stellar observations.
The Arles-Fontvieille monuments are regarded as among the largest and most important megalithic monuments in France. Their particular architecture, rock-cut chambers roofed over with megalithic slabs has also made them among the most enigmatic.
Glyn Daniel argued for the importance of understanding these impressive monuments, writing " It is reasonable to suppose that the builders of the Arles-Fontvieille tombs is a most crucial one - indeed, perhaps the most crucial one - in any analysis of the French megalithic tombs (1960:161)". Other, more recent authors have reiterated the importance of these monuments- Jean Guillaine writes "Par la qualité de leur architecture, ces tombs sont uniques dans tout le sud de la France (1998)".
Glyn Daniel at the Grotte de Corde circa 1960 (Daniel, 1960)
From Daniel, 1960
I should note that my research into the monuments predates that of Michael Hoskin who highlights the rather unique orientation of the Arles/Fontvieille monuments in the direction of the setting sun (2001) and examines the monuments from an archaeoastronomical point of view (and mistakenly, though the error may be his source as he did not visit the Grotte de Corde) . Moreover, while he does not suggest that this orientation might be astronomically functional in the way I have proposed – he does propose that these sites were the center of a culture from which radiated a tradition of westerly oriented graves in a counter-current to the dominant rising sun orientation tradition of the Iberian peninsula and southern France.
Some years ago a hobby while pursuing my Masters at the Ecole des Hautes Etudes en Science Sociales I began studying them to investigate whether their east/west alignment might serve a functional purpose - to allow a ray of sunlight to penetrate them on an around the Spring and Autumn equinox. My hypothesis - that despite being subterranean monument, their position on a slight slope would still allow light to penetrate to the back of the monument has proved correct. I first visited the Grotte de la Source and the Hypogées d'Arnaud-Castellet in 1997 to photograph the equinox sun entering the sites. The following year also visited the Grotte de Bounias at the time of the equinox and the Grotte de la Corde later in the year (and unfortunately as a hobby enthusiast I amateurishly failed to bring a compass and measure the orientation - I and others, including Michael Hoskin, presumed it to be the same as the others, which turns out, importantly, not to be the case).
Photo of the interior of the Grotte de al Source, March 20 or 21, 1997
In 2011 as part of my doctoral research, I returned to the field with a home-made solar time-lapse photograghy set up and recorded showing the light entering the Grotte de la Source on Sept. 16, 2011 and Sept. 23, 2011 (the equinox).
Moreover, having also been able at long last to measure the orientation of the Grotte de Cordes, I have determined that unlike the smaller monuments, it has a seasonal orientation toward the winter solstice, such that for a period of time on and around the winter solstice, light penetrates to the rear of this truly magnificent monument. I have been unable to document this phenomenon photographically during my field research (as this took place at the period of the equinox and my field research funds for travel from Australia are, alas, limited ). HOWEVER- I have constructed a simple model using Google Sketchup which also allows me to visualize the light entering the monument at any time during the year. Thus I have verified using this simulation that light does indeed enter the monument and strike the rear wall at the time of the solstice, and I have received verbal confirmation of this by the land-owner.
My early doctoral research (prior to my discovery of the winter solstice alignment for the Grotte de Corde) was published in the Proceedings of the International Astronomical Union (see the link to the left):
The Archaeastronomy of the megalithic monuments of Arles-Fontvieille: the equinox, the Pleiades, and Orion.
The megalithic monuments of Arles–Fontvieille appear to have been deliberately constructed such that a ray of the setting sun on and around the equinox penetrates the subterranean chamber producing a spectacular light-and-shadow hierophany. Moreover, at one of the sites there is evidence in the form of rock art that observations were also being made of heliacal rising and settings, possibly of both the Pleiades and Orion. The equinox hierophany has been documented at three of the four intact monuments of the group. This phenomenon was probably exploited for sacred ritualistic purposes related to seasonal change and timekeeping by the agricultural people who built the monuments. This evidence has significant importance for understanding these monuments in the context of European megalithism and the wider European Neolithic as well as for understanding their cosmological role within the society that built them.